Three different projects designed to elucidate details of protein interactions at the molecular level are proposed. First, continued studies are planned of the interaction of the hormone-carrying proteins, the neurophysins, with the polypeptide hormones oxytocin and vasopressin, aimed at defining the residues on both the hormones and the proteins involved in their mutual interaction and the thermodynamic contribution of each residue to binding. Other neurophysin studies include investigation of neurophysin-lipid interaction, continued studies of neurophysin primary structure and conformation, and studies of the optical activity of neurophysin disulfides. Second, continued studies of Co(lll)-protein interactions are proposed with the aim of evaluating the usefulness of Co(lll) as a kinetically relatively inert tag of metal-binding sites on proteins which will enable their direct identification. In particular, the Co(lll)-derivatives of bovine carbonic anhydrase-B and carboxypeptidase A will be studied in order to assess the stability of their Co(lll)-ligand bonds to ligand interchange during protein hydrolysis. Finally, studies of the mechanism of iron incorporation into ferritin are planned with the initial aim of identifying residues involved in the ferrous ion oxidase activity of ferritin and defining the mechanism of Zn(ll)-inhibition of iron incorporation.